Speaking as a born and raised Texan, I wouldn’t describe corn as a TexMex staple at all, outside of vegetarian dishes or corn tortillas.
Maybe you have a few kernels in the rice depending on the restaurant, but it’s far from universal and more typical of cuisine from countries south of Mexico (e.g. Salvadorean).
You can generally assume that anywhere serving proper elote is going to be a more true-Mexican street taco type of establishment.